Introduction

This publication provides evidence to support using correctly calibrated and validated digital blood pressure monitors for pregnancy in maternity services. This priority strengthens our existing NHS Long Term Plan and CORE 20Plus5 commitments to transform maternity services across integrated care systems (ICSs), and reduce unequal health outcomes for mums and babies.

Appropriate blood pressure monitoring devices in maternity services reduce morbidity and mortality. This will help save the lives of mums and babies by identifying conditions earlier and more accurately, facilitating appropriate treatment. This means we can reduce the burden of disease while lowering anxiety for mothers and families.

The audience for this document includes maternity services in England, midwife led units and foetal medicine, directors of midwifery, directors of nursing, and clinical directors of obstetrics.  

Background

The long-term health outcomes for mothers and babies exposed to hypertensive disorders could be reduced by avoiding delays in the diagnosis and management of hypertension.

There are 172 mentions of hypertension, blood pressure and eclampsia in the Ockenden report and we know outcomes for mothers and babies can be improved by increasing the quality of diagnosis and hypertensive care in the maternity pathway. This must begin with accurately monitoring baseline and subsequent blood pressure readings, as a diagnostic tool, in the first trimester.

The office of the chief scientific officer for NHS England has reviewed the evidence for the benefits and performance of digital versus aneroid blood pressure monitors and recommends that digital monitors already validated for use in pregnancy, should replace aneroid devices as a primary screening tool. The scale and impact of hypertension in pregnancy is outlined in the NICE clinical knowledge summary of hypertension in pregnancy and listed below:

• Hypertensive disorders occur in 8 to 10% of all pregnancies.
• Chronic hypertension has been reported to complicate 0.6 to 2.7% of pregnancies
• Gestational hypertension is probably under-reported, with recorded rates of 4.2 to 7.9%
• Pre-eclampsia rates range from 1.5 to 7.7% but depend on parity: 4.1% of women in their first pregnancy and 1.7% of women in their second pregnancy have pre-eclampsia
• Haemolysis, elevated liver enzymes, and low platelets (HELLP) syndrome or elevated liver enzymes low platelet syndrome (ELLP syndrome) are observed in around 2 per 100,000 pregnancies overall
• Eclampsia complicates 2.7 per 10,000 births.

1.1 Type of blood pressure monitors (Sphygmomanometers)

There are three types of monitors; mercury, aneroid and digital. Mercury devices have been phased out for health and environmental reasons and replaced with a growing number of aneroid and digital devices.

Compared to aneroid devices, digital versions do not rely on the subjective method of auscultation for Korotkoff sounds and are less vulnerable to mechanical fault and calibration drift. Digital devices require minimal training and are suitable for self-monitoring at home. The advantages of digital devices over aneroid have been clinically evaluated, and there is sufficient evidence that (when calibrated and validated for the intended use) digital monitors are a more suitable alternative to aneroid and mercury devices.

1.2 Pregnancy and blood pressure

The accuracy of blood pressure devices that are validated and calibrated for the general population is not assured, which makes them unsuitable for use in pregnant women. The physiological changes in pregnancy (increased heart rate, stroke volume and reduced total peripheral resistance) are accounted for in devices that are validated and calibrated specifically for use in pregnancy. The British and Irish Hypertension Society provides a published list of devices independently reviewed and approved for home and office monitoring during pregnancy.

1.3 Importance of maintenance on the accuracy of readings

Poor maintenance of blood pressure monitors (regardless of the device type) is strongly associated with inaccurate readings. All devices and cuffs must be examined for visual signs of damage and calibrated at the frequency defined in the manufacturer’s instructions for use. Digital devices are less susceptible to performance errors and require less frequent replacement, calibration and maintenance checks in comparison with aneroid devices.

1.4 Importance of cuff size on accuracy of readings

All blood pressure measurement, regardless of device type, requires the use of a properly sized cuff, depending on the size of the arm of the person that is being measured. Similarly, cuff size is important in considering validation of monitors, and those procuring monitors that have been validated in pregnancy should ensure that a range of cuff sizes that have been validated are also available. 

The British Irish Hypertension Society recommends that: “The bladder of the cuff should fit around at least 80% of the arm but not more than 100%. A cuff that does not fit properly will not give an accurate reading so it is important to use the right size.”

1.5 Device classification and regulation

The MHRA recommend that all devices must be UKCA, CE UKNI or CE marked as a medical device. The configuration and advantages of device types are classified by the Medicines and Healthcare products Regulatory Agency (MHRA) in Blood pressure measurement devices, a guidance document on the purchase, management and use of blood pressure measurement devices.

Cuffless devices and digital applications are the most recent addition to the blood pressure monitoring device market however, the accuracy of cuffless devices are not well established, and are not recommended for clinical use.

1.6 Health inequalities considerations

Using suitable digital blood pressure monitors will improve equity of services for all, including in Black and minority ethnic pregnancies, who are particularly at an increased risk of high blood pressure during pregnancy. As aneroid blood pressure monitors currently in use have been validated and calibrated on predominantly Caucasian males rather than pregnant females of all ethnicities, digital monitors that are calibrated and validated for all pregnant women will help eliminate this bias and address some of the health inequalities.

1.7 Home monitoring in pregnancy and post-natal period

Most pregnant women with chronic or gestational hypertension do not develop pre-eclampsia and associated complications. Hypertensive pregnant women who are otherwise well and postnatal women can be offered a more accurate and acceptable means of monitoring hypertension at home using digital devices.

This could potentially reduce the number of outpatient appointments and bed days. This will also be helpful for people who may find it difficult to attend in-person appointments regularly, such as disabled people, people in rural coastal communities and people who may feel uncomfortable in clinical environments.

Recommendations

Five recommendations are outlined below which have been developed from the current research evidence by the office of the chief scientific officer and other expert contributions. Implementing these recommendations will enable optimisation of the use of suitably validated and calibrated digital blood pressure monitors in home or hospital settings. This will improve the care for mums and their babies.

1. Digital devices should replace aneroid devices as the diagnostic screening tool in maternity services.
2. Digital blood pressure assessment should take place at every antenatal appointment, including the booking appointment.
3. Digital devices must be regulatory approved and validated for use in pregnant populations.
4. Home and office use of digital blood pressure monitors should be considered for all pregnant women as an early warning signal for hypertension prevention.
5. All NHS and social care organisations, including community pharmacies, can use the Automated Blood Pressure Monitor Dynamic Purchasing System (DPS) to procure larger volumes of approved blood pressure machines at competitive prices. The DPS enables quicker, easier, and more informed procurement processes for NHS and other organisations.

Useful links

1. NICE Clinical Knowledge summary, Hypertension in Pregnancy (Prevalence)
2. Recommendations | Hypertension in pregnancy: diagnosis and management | Guidance | NICE
3. Medicines and Healthcare products Regulatory Agency (MHRA). Guidance on the purchase, management and use of blood pressure measurement devices
4. The British and Irish Hypertension Society Recommended BP monitors.
5. Final report of the Ockenden review. Findings, conclusions and essential actions.
6. United States National Library of Medicine, Effect of Self-monitoring of Blood Pressure on Blood Pressure Control in Pregnant Individuals With Chronic or Gestational Hypertension: The BUMP 2 Randomized Clinical Trial – PubMed
7. United States National Library of Medicine, Effect of Self-Monitoring of Blood Pressure on Diagnosis of Hypertension During Higher-Risk Pregnancy: The BUMP 1 Randomized Clinical Trial — Nuffield Department of Primary Care Health Sciences, University of Oxford
8. United States National Library of Medicine, Exploring the potential for introducing home monitoring of blood pressure during pregnancy into maternity care:.

Digital and aneroid blood pressure monitors – list of experts consulted and contributors

• Professor Andy Shennan, Consultant Obstetrician, Kings College London
• Professor Anna David, Consultant in Obstetrics and Maternal Fetal Medicine, University College London
• Angela Douglas, Deputy Chief Scientific Officer, Medical Directorate NHS England
• Professor Edward Johnstone, Consultant Obstetrician, Manchester University NHS Trust
• Eleri Adams, GIRFT Lead, Neonatal NHS England
• Professor Jenny Myers, Consultant Obstetrician, Manchester University NHS Trust
• Lisa Anderson, Heart Failure Consultant, St George’s University Hospitals NHS Trust London
• Lucy Bonsall, Senior Project Manager CVD Prevention Clinical Policy Unit, NHS England
• Matthew Jolly, National Clinical Director for Maternity Programme, NHS England
• Melanie Smith, Scientific Advisor Office of the Chief Scientific Officer, NHS England
• Ngozi Edi-Osagie, National Clinical Advisor for Neonatal Services, NHS England
• Professor Richard McManus, Nuffield Department of Primary Care Health Sciences, University of Oxford
• Sarah Cooper, Cardiac Clinical Scientist, South-West Scientific Regional Lead
• Sue Robinson, Senior Delivery Manager NHS@Home, NHS England.

Publication reference: PRN00020